Long distance speaker devices installed in wide spaces such as an air port lobby, music hall, and gymnasium include one in which a vertically long front panel is provided with a line array speaker, and the front panel is gently curved so as to move back a lower end. By using such a long distance speaker device, a substantially uniform sound field can be formed over a wide range from a long distance to a short distance.
It is considered that if such a curved state of the front panel can be virtually reproduced by delay control of each speaker, for example, a short distance speaker device in which a line array speaker is provided on a flat plate front panel can be used as the long distance speaker device. It is also considered that depending on an installation location or surrounding environment, a curved shape of the virtual front panel can be changed to form a shape of the sound field.
However, in the case of attempting to achieve the gentle curve of the front panel by the delay control of each speaker, a very small delay time should be accurately controlled. For example, in the case of a sampling rate of 48 kHz, a sampling period is 20 μs; however, to achieve the gentle curved state of the front panel, a delay time of each speaker should be controlled with an accuracy of 1 μs or less, and therefore a much smaller delay time than the sampling period should be controlled. On the other hand, in the case of attempting to provide a very small delay less than the sampling period to a digital sound signal by digital signal processing, there arises a problem that a load on the signal processing becomes excessive.
In order to provide the delay less than the sampling period to the sound signal by the digital signal processing, some sort of interpolation process should be performed; however, when only linear interpolation having a relatively small calculation load is performed, there arises a problem that reproducibility in a high range is considerably reduced. On the other hand, in the case of combining oversampling and linear or polynomial interpolation, there arises a problem that a low pass filter having a sharp cutoff is further required in order to remove aliasing, and therefore a calculation load becomes excessive.
Meanwhile, there has been proposed a speaker device that controls an output delay of each of speakers constituting a line array speaker (e.g., Patent Literature 1). The speaker device disclosed in Patent Literature 1 is one that is intended to control directivity, in which it is considered that a digital filter is provided corresponding to each of the speakers, and an output delay of each of the speakers is controlled so as to give rise to a certain delay time difference between adjacent speakers. In the case of the directivity control that simply changes an aiming direction horizontally as described, the delay time difference between adjacent speakers is sufficiently large as compared with the sampling period of the sound signal, which can be easily achieved by selecting a delay time of each of the speakers from integral multiples of the sampling period.